The invention relates to glass/plastic compounds based on thermoplastic, and to a process for producing them.
Reinforced plastics materials, mainly based on thermoplastics, are used in electrical engineering and electronics to produce appliances and components. The reinforced thermoplastics used are usually thermoplastic compounds which contain glass fibers.
It is known that, on account of external contamination of the insulation caused by deposits of dust and chemicals or other contamination, a current, known as a tracking current, can flow on insulating-material surfaces when a voltage is applied. In the case of plastic insulating materials, this leads to the formation of a conductive tracking path on the plastic surface, which is attributable to thermal degradation products formed from the polymer matrix. However, the insulating action of the plastic is thus lost. The voltage level at which a conductive tracking path is formed is dependent on the material. This phenomenon, i.e. the occurrence of tracking currents and the formation of tracking paths, limits the possible uses of the various groups of polymer materials as electrical insulants to a certain extent, since in many cases a high tracking resistance is also demanded for use in electrical engineering as well as a high electrical strength.
Particularly in the case of electrical and electronic parts and components, high demands are imposed on the tracking resistance, i.e. the CTI value (CTI=Comparative Tracking Index). For example, in the case of relay components for actuators and caps, CTI values of at least xe2x89xa7125 V, and generally even xe2x89xa7175 V, are required. For relay base bodies in what are known as xe2x80x9cwhite goodsxe2x80x9d, this requirement is generally xe2x89xa7175 V, and for use in the automotive sector this value is at least xe2x89xa7225 V. For other applications in electrical engineering or electronics, for example in housings, the requirements may even be significantly higher still.
It is known that high-temperature thermoplastics, i.e. high-performance thermoplastics, apart from partially aromatic polyamides, have only a noticeably low tracking resistance of approx. 100 to 175 V. This low tracking resistance may even be reduced further when reinforcing materials, such as glass fibers, are added. As a result, many possible applications for the high-temperature thermoplastics remain out of reach.
It is an object of the invention to provide glass/plastic compounds based on thermoplastics which have a high tracking resistance.
According to the invention, this is achieved by glass/plastic compounds which contain the following components:
a low-melting sulfophosphate glass of the following composition (in mol %): 4 to 10% of Li2O, 4 to 10% of Na2O, 4 to 8% of K2O, 1 to 2% of CaO, 35 to 37% of ZnO, 0 to 3% of La2O3, 19 to 22% of P2O5 and 19 to 22% of SO3,
a high-performance thermoplastic, and
an organic additive and/or a mineral filler, and if appropriate also
carbon black and/or a sterically hindered phosphite or phenol.
A xe2x80x9clow-meltingxe2x80x9d sulfophosphate glass is understood as meaning a glass with a low glass transition temperature Tg, in particular a glass with Tg less than approx. 500xc2x0 C. A xe2x80x9chigh-performance thermoplasticxe2x80x9d is a high-performance polymer, and specifically, in the present case, a heat-resistant polymer (xe2x80x9chigh-temperature resistant polymerxe2x80x9d). This is important because both the temperature during production of the compounds and the working temperature (of the compounds) is  greater than 300xc2x0 C.
The glass/plastic or glass/polymer compounds according to the invention have a high tracking resistance: the CTI value may be up to 250 V and above. This opens a wide range of applications for the novel high-performance compounds in electrical and electronic parts and components, i.e. a wider range of uses. It is also important that the high tracking resistance is achieved with even relatively small amounts of additives, which has a highly positive effect on the free-flowing properties and the mechanical properties.
The German Patent Application bearing the reference number 199 60 548.3 (application date: Dec. 15, 1999) describes glass/plastic compounds based on thermoplastic which contain the following components:
a low-melting sulfophosphate glass of the following composition (in mol %): 4 to 10% of Li2O, 4 to 10% of Na2O, 4 to 8% of K2O, 1 to 2% of CaO, 35 to 37% of ZnO, 0 to 3% of La2O3, 19 to 22% of P2O5 and 19 to 22% of SO3, and
a high-performance thermoplastic.
Compared to these compounds, the glass/plastic compounds according to the invention, which contain an organic additive and/or a mineral filler, have a CTI value which is increased by 50 to 100 V. If these compounds additionally contain carbon black and/or a sterically hindered phosphite or phenol, the tracking resistance is increased further, specifically to CTI values of xe2x89xa7250 V.
In addition to the improved tracking resistance, the glass/plastic compounds according to the invention also have good mechanical and thermal properties and good processing properties, in particular a good ability to flow, even with a high filler content, i.e. a high glass content. Moreover, they are distinguished by an excellent chemicals resistance, in particular to water, acids and bases, and specifically, which is surprising, without the addition of stabilizers. Furthermore, these glass/plastic compounds have an excellent resistance to abrasion and the materials can be recycled without problems, since there is no shortening of the glass component as is the case in compounds reinforced with glass fibers.
The sulfophosphate glasses which are present in the glass/plastic compounds according to the invention have a glass transition temperature of 250xc2x0 C. less than Tg less than 280xc2x0 C. It is preferable for a sulfophosphate glass of the following composition (in mol %) to be used in the compounds: 4.9% of Li2O, 9.4% of Na2O, 7.1% of K2O, 1.6% of CaO, 36.6% of ZnO, 20.0% of P2O5 and 20.4% of SO3. A glass of this type has a glass transition temperature of 268xc2x0 C. By way of example, another glass has the following composition (in mol %): 9% of Li2O, 5% of Na2O, 7% of K2O, 1.6% of CaO, 37% of ZnO, 20.4% of P2O5 and 20% of SO3 (Tg=280xc2x0 C.). By way of example, a further glass has the following composition (in mol %): 4.8% of Li2O, 9.2% of Na2O, 6.9% of K2O, 1.6% of CaO, 35.9% of ZnO, 2.0% of La2O3, 19.6% of P2O5 and 20.0% of SO3 (Tg=275xc2x0 C.).
The high-performance thermoplastic used is advantageously a polyether ether ketone (PEEK), a polyetherimide (PEI), a polyphenylene sulfide (PPS), a partially aromatic polyamide, such as polyphthalamide (PPA), or a liquid-crystal polymer (LCP). In these polymers, the glass transition temperature of the glass component is matched to the working temperature of the thermoplastic material. Further high-performance thermoplastics which can be used are polyaryl ether ketones (PAEK) in general, for example polyether ketones (PEK), and polysulfones (PSU), in particular polyethersulfones (PES) and polyphenylene sulfones (PPSU).
The level of the glass component, i.e. of the sulfophosphate glass, in the glass/plastic compounds is preferably 15 to 60% by weight, based on the level of sulfophosphate glass and high-performance thermo-plastic. For certain applications, however, the glass contents may be up to 80% by weight. The compounds may also contain standard additives, such as coloring pigments and stabilizers. There are possible applications in, for example, sensors, actuators, plug connectors and relays.
The organic additive is preferably melamine cyanurate, a polysiloxane or a halogenated flame retardant, such as poly(haloaryl (meth)acrylate) and halogenated polystyrene. Further additives which can be used are elastomers, for example olefinic elastomers, rubbers, polyamides, fluoropolymers and organosilanes, such as 3-mercaptopropyl-trimethoxysilane.
The mineral filler is preferably mica, calcium sulfate (CaSO4) or a zinc borate, such as 4ZnO.B2O23.H2O. However, other suitable fillers include magnesium hydroxide, aluminum hydroxide, aluminum borates, barium sulfate, antimony trioxide, titanium dioxide, calcium phosphate, pyrophosphates, in particular sodium and potassium pyrophosphate, ammonium polyphosphates and talc.
The level of organic additive and/or mineral filler in the glass/plastic compounds is advantageously 5 to 40% by weight, in particular 5 to 15% by weight, in each case based on the total weight. The level of carbon black is advantageously 0.1 to 1.0% by weight, in particular 0.2 to 0.5% by weight, and the level of sterically hindered phosphite or phenol is 0.5 to 1.5% by weight, in particular approx. 1% by weight, in each case based on the total weight.
Examples of suitable phosphites, i.e. esters of phosphoric acid, are compounds such as tris-(2,4-di-tert.-butylphenyl)phosphite. Examples of suitable phenols are (3,5-di-tert.-butyl-4-hydroxyphenyl)-propionate, such as the corresponding propionates of octadecanol and pentaerythritol.
The production of the glass/plastic compounds according to the invention takes place in such a manner that first of allxe2x80x94at elevated temperaturexe2x80x94a masterbatch with a glass content of 60 to 90% by weight is produced from the two components sulfophosphate glass and high-performance thermoplastic. In the process, it was surprisingly discovered that using glass particles (glass grains) with a diameter of xe2x89xa61.5 mm in the masterbatch resulted in glass structures in the xcexcm and sub-xcexcm range with a uniform distribution.
Then, in a second process step, the further processing takes place in such a manner that, by adding further high-performance thermoplastic to the masterbatchxe2x80x94at elevated temperaturexe2x80x94the glass content is reduced to 15 to 60% by weight. The structure and homogenous distribution of the glass particles are not affected, i.e. are retained. Surprisingly, control experiments showed that the structure size and distribution of the type described are not obtained if the process proceeds directly from a batch with a glass content of, for example, 15%. Rather, uniformly distributed glass structures, even in the nm range, can only be achieved by starting from a masterbatch with a high proportion of the special sulfophosphate glass in a high-performance thermoplastic.
At the same time, in the second process step, an organic additive and/or a mineral filler is also added. If appropriate, carbon black and/or a sterically hindered phosphite or phenol may also be added.
The glass/plastic compounds according to the invention are produced at elevated temperature, preferably at approximately 320 to 420xc2x0 C. During the production of the compounds, it is also possible to set the structure of the glass particles (isotropic/anisotropic) by means of the processing conditions.
Moreover, the compounds are distinguished by good bonding of the glass
component to the thermoplastic material, as demonstrated in particular by the good chemicals resistance.
Since it is possible to start from relatively coarse particles of a sulfophosphate glass, the particle size being xe2x89xa64 mm, preferably xe2x89xa61.5 mm, the process according to the invention thus makes it possible to achieve inexpensive production even of glass/plastic compounds in which the glass particles are distributed uniformly and homogeneously in a high-performance thermoplastic and, moreover, can be set in a controlled manner even down to the nm range. This is achieved by using the viscosity of the individual components and the processing conditions, in particular the working temperature; the viscosity ratio of plastic to glass is generally approximately 1:1000. Compounds of this type are particularly suitable for the production of appliances and components for electrical engineering and electronics. This is because in these applications the important demands with regard to materials and processing properties are met and fault-free operation is ensured. In appliances and components used in electrical engineering and electronics, the compounds also allow the number of materials used to be reduced considerably, in particular with regard to the plastics, possibly even to the extent of using single grades. This allows inexpensive recycling of the materials while maintaining the filler properties.